<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        .cont{margin: 0 auto;background: #ccc;position: relative;}
        .cont::after{content: "";display: block;clear: both;}

        .box{float: left;padding: 6px;}

        .imgbox{border: solid 1px black;padding: 6px;border-radius: 6px;}
        
        .imgbox img{width: 200px;display: block;}
    </style>
    <script src="data/data.js"></script>
    <script>
        // W1. 准备数据
        // W2. 绑定滚动事件
            // W3. 判断页面是否到底（滚动的距离+可是区域的高度 == 最后一个元素的top）
            // W4. 加载新数据，渲染新页面
            // W5. 重新执行瀑布流效果


        onload = function(){
            new Waterfall;
        }
        
        class Waterfall{
            constructor(){
                // 1.选择元素
                this.box = document.querySelectorAll(".box");
                this.cont = document.querySelector(".cont");

                this.clientH = document.documentElement.clientHeight;
                

                this.heightArr = [];

                // 2.补全布局
                this.init();

                this.addEvent();
            }
            addEvent(){
                var that = this;
                onscroll = function(){
                    var scrollT = document.documentElement.scrollTop;
                    if(that.clientH + scrollT > that.scrollH-300){
                        that.render()
                    }
                }
            }
            render(){
                for(var i=0;i<data.length;i++){
                    var img = document.createElement("img")
                    img.src = data[i].src;
                    var imgbox = document.createElement("div")
                    imgbox.className = "imgbox";
                    var box = document.createElement("div")
                    box.className = "box";
                    imgbox.appendChild(img);
                    box.appendChild(imgbox);
                    this.cont.appendChild(box);
                }
                // 初始化所有
                this.box = document.querySelectorAll(".box");
                this.heightArr = [];
                // 重新渲染瀑布流结构
                this.firstLine();
                this.otherLine();
            }
            init(){
                // 计算一行最多能放几个，再计算最大宽度
                this.clientW = document.documentElement.clientWidth;
                this.boxW = this.box[0].offsetWidth;
                this.maxNum = parseInt(this.clientW / this.boxW)
                this.cont.style.width = this.boxW * this.maxNum + "px";

                // 3. 区分第一行
                this.firstLine()
                // 4. 区分其他行
                this.otherLine();
            }
            firstLine(){
                // 5. 获取所有元素的高度，存起来
                for(var i=0;i<this.maxNum;i++){
                    this.heightArr.push(this.box[i].offsetHeight);
                }
            }
            otherLine(){
                for(var i=this.maxNum;i<this.box.length;i++){
                    // 6. 拿到第一行所有的高度
                    // console.log(this.heightArr)
                    // 计算最小值和最小值的索引
                    // var min = getMin(this.heightArr);
                    // var min = Math.min.apply(null,this.heightArr);
                    var min = Math.min(...this.heightArr);
                    var minIndex = this.heightArr.indexOf(min);
                    // console.log(minIndex);
                    // 7. 设置元素的定位
                    this.box[i].style.position = "absolute";
                    // 8. 设置元素的top和left
                    this.box[i].style.top = min + "px";
                    this.box[i].style.left = minIndex * this.boxW + "px";
                    // 9. 修改最小值
                    this.heightArr[minIndex] += this.box[i].offsetHeight;
                }
                this.scrollH = document.documentElement.scrollHeight;
            }
        }




        function getMin(arr){
            // 先对数组进行截取（为了深拷贝）
            // 然后对截取出的新数组排序
            // 找第0位
            // 返回出去
            return arr.slice(0).sort((a,b)=>a-b)[0];
        }
        
    </script>
</head>
<body>
    <div class="cont">
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/4.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/2.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/3.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/5.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/1.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/6.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/7.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/8.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/9.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/10.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/4.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/2.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/3.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/5.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/1.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/6.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/7.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/8.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/9.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/10.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/4.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/2.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/3.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/5.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/1.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/6.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/7.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/8.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/9.jpg" alt="">
            </div>
        </div>
        <div class="box">
            <div class="imgbox">
                <img src="../imgs/10.jpg" alt="">
            </div>
        </div>
    </div>
</body>
</html>